Richie Dixon has brought wingers Rory Kerr and Michael Bartlett in from the cold to add some firepower to the Warriors.
And No.8 Petrie reckons the return of Dixon will have a positive effect on their play.
He explained: "Because Richie hasn't been involved with training this season he hasn't really changed much and has given us a free rein. That will be good for the squad. The way we have been doing things this season has been quite strict and we should now be able to play a far more expansive game. There will be no shackles on us as before."
"Spinning the ball wide is something Glasgow have been renowned for doing in seasons gone by and it would be nice to put this week behind us by scoring some tries. In the past we have scored a lot of points and racked up some good wins by trying to go outside teams and hopefully we can repeat that tonight. It has been quite difficult to prepare properly with everything that has been happening this week. It is up to us to try and focus. Of course, we can still do it. But all the players can do is concentrate on going out and trying to win the match. After that, we will see what happens."